The present invention relates to a capillary device for conducting immunoassay tests. More particularly, the present invention relates to a capillary device for conducting an immunoassay test which device contains the reagents necessary for carrying out the test and confines the reagents and sample tested within the device during the course of the test.
Immunoassay tests are used for the detection in body fluids of a wide variety of compositions including antigens, antibodies, infectious agents and hormones. The purpose of the immunoassay test is to measure the degree of interaction between an antigen and its corresponding antibody.
It has been proposed to utilize various wet chemistry processes wherein the immunoassay interactions are conducted in tubes or plates containing multiple compartments wherein an antibody or an antigen is coated in the surface of the tube or compartment. The use of these devices requires a number of steps of applying and then removing reagents from the compartments or tubes and requires that the volume of these reagents be accurately measured. In addition, relatively large samples are required to conduct the immunoassay test in these devices. An additional serious problem associated with these wet chemistry techniques is the disposal of biological liquids which may contain infectious agents.
European Patent Application 0,142,914 discloses a self-contained microassay card which houses a wash liquid, a plurality of separated reagents and a microassay rod upon which the assay is effected. The use of the card requires the use of a syringe in order to introduce a precise volume of the sample into the chamber housing the microassay rod. This requires a separate step of measuring the precise volume desired. In addition, since the syringe is required to deliver the sample under pressure, the chamber housing the microassay rod must be closed to avoid loss of sample which in turn requires a precision fit plug. Since no provision is made in the device for a filter means, whole blood cannot be processed thereby requiring an additional step for separating the cellular components from the plasma components prior to initiating the microassay. Lastly, the device requires the precise positioning of pressure means at various locations on the outside surface of the device in order to effect proper sequencing of reagents to contact sample components during the test. The requirement of precise positioning at the proper time during the test introduces a major source of error for the test.
European Patent Application 0 073,513 discloses a device for conducting assays which includes a rotor upon which are positioned a plurality of elements which house reagents in separate compartments. The compartments are located within an element at different radial positions on the rotor and at least one compartment is in fluid communication with a sample application chamber located at the radially innermost position of the compartment. A mixing chamber which allows for the introduction of a liquid reagent is located within a compartment at a radially intermediate position and a measurement chamber is located at the radially outermost position of the compartment. Liquid sample and/or liquid reagent are moved from compartment to compartment and eventually to the measurement chamber by means of conduits connecting the compartments and centrifugal force caused by rotating the rotor. This mode of operation requires that the conduits be of precise size and that the rates of rotation be precisely controlled otherwise liquid flow into the wrong compartments occurs. These requirements introduce a serious source of error in the assay.
P.C.T. publication number W082/02601 discloses a solid phase assay system which utilizes a porous solid matrix such as treated paper or a mat of fibers. A binding material is reacted with its antibody within the solid matrix to immobilize the reaction product within the matrix. The amount of binding material and its antibody that are reacted must be very accurately controlled using accurate volumetric micropipettes. Solutions of analyte and labelled indicator then are applied to the matrix to effect the assay either as a competitive assay or as a sandwich assay. Unbound labelled indicator is removed from the matrix by a chromatographic procedure utilizing a solvent. The concentration of labelled indicator in the reaction zone then is measured. This assay is undesirable since it requires measuring precise volumes, manual washing steps and the pipetting of reagents. It is also unsuitable for assaying whole blood.
European Patent Application 0 186 100 discloses a solid phase assay which utilizes a fiber matrix coated with a polymer capable of retaining a reagent which binds with an analyte of interest. A second reagent is bound to the bound analyte and a third reagent is introduced which, in the presence of the second reagent, produces a detectable response. The disadvantage of this assay is that it requires precise volumes of reagent and sample which requires time-consuming volume measurement steps.
U.S. Pat. No. 4,426,451 discloses a device for conducting an assay which utilizes two continuous capillary zones in fluid communication with each other. A narrow passageway is provided between the two zones in order to temporarily stop liquid flow between the zones. Liquid transfer between the zones is initiated by a pulse or pressure and completed by capillary action to the zone having the smaller capillary. The device is useful for conducting competitive assays or for separating whole blood into a cellular component and a plasma component. Since no means are provided for at least one washing step and since separation of bound species from unbound species relies solely upon capillary action, incomplete separation of bound from unbound species occurs. This leads to error in the assay. In addition, the device does not permit conducting a sandwich assay.
It has been proposed in French Patent Application Number 7712933, published Nov. 24, 1978 to conduct immunoassays in a capillary tube. However, no means are provided for filling the capillary and for eliminating the need for removing reagents and reaction products from the capillary. Thus, the problem of disposing infectious materials is still present.
P.C.T. publication number W086/06488 discloses a test apparatus for performing chemical, clinical diagnostic and like tests. The apparatus includes a housing, a sample receiving area and a plurality of rupturable containers in recesses within the housing. The containers include the predetermined amount of one of the specific reagents which are required for the test. A duct or channel connects each area with the sample receiving area where the sample is located. A member is provided in association with each container to enable the container to be ruptured when addition of the specific reagent is required in the test. This assay apparatus does not include a self-metering sample application element. Instead it requires an operator to pipette a precisely measured volume of the sample onto the sample receiving membrane. The membrane thickness is not precisely defined and therefore the apparatus is not capable of providing very accurate quantitative results. Further, the fluid stream in the apparatus is not very well defined with the result that very high volumes of wash liquid, e.g., about 1-2 ml, must be used because the liquid must cover the entire test element.
It would be highly desirable to provide a means for conducting immunoassay tests under conditions which require only small samples, which provide accurate test results, which eliminates the need for measuring precise volumes of reagents, which permits the testing of whole blood and which eliminates the problems associated with disposing of infectious liquids.